bin_yb

Name

bin_yb - binarize a gray-scale band using Yanowitz and Bruckstein`s method

Syntax

 #include <xite/binarize.h>

 int bin_yb( IBAND inband, IBAND outband,
    int threshold, double beta,
    int max_iterations );

Description

The input band inband is binarized using the method of Yanowitz and Bruckstein. The result is returned in outband.

A potential surface passing through the image at local maxima of the gradient image is used as a thresholding surface. The gradient magnitude image is computed, using for example Sobel`s edge operators. This image is thresholded using threshold. However, if threshold == 0, Otsu`s method is used. The thresholded image is thinned to one-pixel wide lines, to identify edge pixels. The original image is smoothed by a (3x3) mean filter to remove stochastic noise. A potential surface is constructedby an iterative interpolation scheme. The interpolation surface is made to pass through the edge pixels. An interpolation residual R(x,y) is calculated for each non-edge pixel, and the new pixel value P(x,y) at iteration n is calculated as

  P[n](x,y) = P[n-1](x,y) + (beta * R[n](x,y)) / 4

Yanowitz and Bruckstein recommended to use 1.0 < beta < 2.0 for fast convergence (over-relaxation). However, we found that by using beta > 1.0, P(x,y) started to diverge after 5-10 iterations. So beta <= 1.0 must be used, and beat = 1.0 works well. A maximum number of max_iterations is perfromed.

Next, the image is binarized using the thresholding surface. In the original algorithm, so-called "ghost" objects are removed by a validation step. This validation step is in a separate library function named rem_ghost.

Restrictions

inband and outband must have pixel type unsigned band.

References

S.D. Yanowitz & A.M. Bruckstein: "A New Method for Image Segmentation", Comput. Vision Graphics Image Proc., vol 46, no 1, pp 82-95, April 1989.

Return value

 0 : ok
 1 : Bad input pixel type
 2 : Bad output pixel type

Files

src/binarize/bin_yb.c

Author

Řivind Due Trier

Id

$Id: bin_yb.c,v 1.16 1997/01/14 15:46:59 svein Exp $